This invention relates to a seal assembly and more particularly to a seal assembly for a linkage, such as a track linkage, which is subject to oscillatory motions.
U.S. Pat. No. 3,841,718 discloses a seal assembly for a track linkage in which an outer link and an inner link have overlapping ends joined in a pin joint connection providing for a relative rotation about a pin which extends through the ends of both links, the pin being connected to the outer link and rotating within a bushing connected to the inner link, the bushing having an end face facing a counterbore in the inner face of the outer link. The seal assembly comprises a crescent-shaped seal ring and a load ring partially encompassed by the seal ring. The crescent-shaped seal ring has a driving flange, a sealing flange and a thin flexible hinge section connecting the two flanges. The load ring fits within the seal ring to press the driving flange into an interference fit with the counterbore walls to cause the driving torque to be transmitted through the seal ring, while the load ring transmits most of the force with which the sealing flange is urged into sealing engagement with the end face of the bushing.
The seal ring is made of a tough wear-resistant or abrasion-resistant material and the load ring is made of an elastomeric material having good spring characteristics over a wide operating temperature range.
While the above described seal assembly has proved effective in practical applications, it has been found that the seal assembly poses some problems. Since the sealing flange is urged in sealing contact with the end face of the bushing, the end face tends to wear to produce a shallow annular groove thereon when it is used for a long period. As a result, when the bushing is reinstalled by turning the other way around after a considerable of service time as in a common practice in the art concerned, even if a new seal assembly is installed in the counterbore it is difficult to obtain a good sealing effect due to the presence of the shallow annular groove on the end face of the bushing, thus resulting in leakage of lubricant and intrusion of dirt therethrough. Although it is necessary to finish the end face of the bushing under 1 .mu.m in order to improve the durability of the seak assenbly, lapping of the end face is not easy to perform and results in an inefficient working.
Besides, when the hardness of the end face of the bushing is raised by heat treatment in order to improve wear-resistant characteristics thereof, toughness of the bushing itself will deteriorate.
Therefore there has been a practical limit to the improvement of the wear-resistant characteristics of the end face of the bushing.